Liquid scintillation counting is an important analytical tool with extensive applications in medicine and in basic and applied research. The level of the radioactivity of the waste is relatively low, representing about 8 curies used per year on a national level with low energy beta emitters such as carbon fourteen and hydrogen three being the major contributors to such emissions.
While each LSC analysis uses a relatively small amount of liquid, in the order of 10-15 milliliters, a great number of such analyses are done each year, and the total volume of resulting liquid is substantial and presents a substantial disposal problem.
The LSC cocktail comprises an aromatic liquid, such as toluene, xylene, or benzene, with a small amount of an organic fluor such as PPO, PBD, PBBO, and other oligophenylenes known to those skilled in the art. By placing a radioactive labelled compound within the energy sensitive cocktail, the radioactivity of the compound can be measured.
At the present time, the only repository which will accept organic radioactive wastes in in Richland, Wash., and that site is scheduled to be discontinued sometime in 1982. Burning the waste is not a satisfactory disposal method because radioactive elements may be dispersed in the atmosphere. Transporting liquid waste to the state of Washington is obviously hazardous and unsatisfactory. As a result, liquid LSC waste is now being accumulated by the users and there is no satisfactory method of disposing of it. Unless a suitable and safe method is found, it is probable that the use of liquid scintillation counting will have to be drastically curtailed and permanently restricted.
The object of the present invention is to provide a method of dealing with and disposing of the wastes resulting from liquid scintillation counting analyses.
In accordance with my invention, I have discovered that LSC wastes in substantial amounts can be made into a dispersion with water in which the continuous phase is water and then mixed with Portland cement or the like to make a permanent, solid, concretelike material in which the LSC waste is well distributed and which has good compressive strength, leach, and heat resistance so that it can be transported in the solid state and stored at suitable radioactive solid storage sites.
As a general proposition, a hydrophobic organic material is not compatible with cement and, if it mixes with the cement at all, it does not mix with it in any sort of a uniform manner.
In cementing of oil wells, it is standard practice to make cement/oil/water emulsion mixtures and pump them down the well as a slurry to seal up the well. The mixture has to be fluid, and usually is compounded so that it takes an extended time to set up.
It has even been proposed that a water-in-oil emulsion be made up and mixed with cement and radioactive waste and pumped down into cavities in the ground for storage. The concept is that the cement does not begin to set up until the emulsion breaks and the water can interact with the cement. Reference is made to U.S. Pat. No. 3,62,274.
In accordance with my invention, I have discovered that more LSC liquid organic material can be incorporated in a cement than would have been thought possible, and that for reasons not now clear to me, the addition of organic material up to a certain point actually improves the compressive strength of the resulting compound. In accordance with my invention, for every 100 grams of cement, I use about 32 milliliters of water, between about 20 and 30 milliliters of the LSC aromatic liquid waste, and about 4 milliliters of a dispersing agent such as Triton X-100.